The Epoch of the Constellations on the Farnese Atlas and Their Origin in Hipparchus’s Lost Catalogue

The Farnese Atlas is a Roman statue depicting the Titan Atlas holding up a celestial globe that displays an accurate representation of the ancient Greek constellations (see Figures 1 and 2). This is the oldest surviving depiction of this set of the original Western constellations, and as such can be a valuable resource for studying their early development. The globe places the celestial fi gures against a grid of circles (including the celestial equator, the tropics, the colures, the ecliptic, the Arctic Circle, and the Antarctic Circle) that allows for the accurate positioning of the constellations. The positions shift with time due to precession, so the observed positions on the Farnese Atlas correspond to some particular date. Also, the declination of the Arctic and Antarctic Circles will correspond to a particular latitude for the observer whose observations were adopted by the sculptor. Thus, a detailed analysis of the globe will reveal the latitude and epoch for the observations incorporated in the Atlas; and indeed these will specify enough information that we can identify the observer. Independently, a detailed comparison of the constellation symbols on the Atlas with those from the other surviving ancient material also uniquely points to the same origin for the fi gures. The Farnese Atlas fi rst came to modern attention in the early sixteenth century when it became part of the collection of antiquities in the Farnese Palace in Rome, hence its name. The statue was later transferred to the museum in Naples now called the Museo Archeologico Nazionale di Napoli. It is carved in white marble and depicts the bearded Atlas crouched down on one knee with a cloak over his shoulder and holding the celestial globe on his shoulder with both hands. The globe is 65cm in diameter. Its top has a substantial hole knocked into it and this has obliterated the constellations of Ursa Major and Ursa Minor. A total of 41 constellations are depicted, each drawn in positive relief as the classical fi gure, with no individual stars shown. Art historians conclude that the statue is a Roman copy from the second century A.D. of a Greek original dating to before the birth of Christ. What is the date of the observations used for depicting the constellation positions on the Farnese Atlas? A very wide range of plausible answers is possible. First, the Roman sculptor could have updated the constellation positions with his own observations (or those of a contemporary), hence suggesting a date of c. 150 A.D. Second, the Roman sculptor could have used the latest star catalogue to place the constellations accurately onto the coordinate grid of the sky, and this would be from the Almagest of Ptolemy, JHA, xxxvi (2005)